With scaling to the nanometer regime and improvements in trans-conductance and parasitics, many sophisticated integrated systems can now be implemented in CMOS. However, as feature sizes shrink, new challenges arise, as process, voltage, and temperature (PVT) variations grow larger and more difficult to control. For instance, the small number of dopants in the channel becomes an important source of randomness, rendering traditional techniques (e.g., common-centroid or interdigitated designs) ineffective. From an RF system perspective, such variations can be detrimental since parameters such as gain, phase balance, and common-mode rejection are not well controlled.
Process variations in the fabrication of integrated circuits lead to variations in the operating parameters or characteristics exhibited by multiple exemplars of the same circuit or device, including those made on the same fabrication line. These variations can result in divergent operation of what should be identical devices. One problem that this can create is the necessity to “trim” or adjust circuits to achieve acceptable operation. In the worst of cases, the variation can result in the need to reject or to discard chips that fall outside a desired operational envelope.
In addition, the operational parameters or characteristics exhibited by any one exemplar of a circuit or device can change as the circuit or device ages, as operating conditions such as ambient or operating temperature vary, or as external operating parameters such as supply voltage vary. The operational parameters or characteristics can in various embodiments be dependent on frequency.
A 10 bit phase rotator that can be used as a component has been described in H. Wang and A. Hajimiri, “A wideband CMOS linear digital phase rotator,” in Proc. IEEE CICC, Sep. 2007, pp. 671-674. This paper discusses in some detail the issues of phase and amplitude variation.
There are prior art devices that attempt to perform self healing using an applied signal of interest.
There is a need for systems and methods that allow circuits and devices that exhibit divergent operating parameters or characteristics to “self heal” or to self correct when varying operating parameters or characteristics are present.